@Callimanco I think I can clear some things up, I've given this lots of thought 
Dennis Penni's killed Jennifer Saunders because he was being paid by the sugar daddy to find out who the blackmailers were and stop them. He needed the money to pay for specialists to assess his daughter who had a mystery illness, later revealed to be that her mum was feeding her rat poison
Yes
The dad and the detective framed Dennis for killing Tripp and, presumably, Corinne?? Thereby leaving said daughter in the clutches of evil Mum which didn't seem to worry them but then I don't recall who knew and if said Mum was ever reported to the police. The police were shown in the background with IIRC the teenagers saying the police know and she will be safe now, or something to that effect.
What was the point of the young black woman who constantly faked pregnancies and why did her husband hit the Dad when he opened the door to him? When her husband visited their house, he hit him and told him to stay away from his family. When he later met up with pregnancy faker, he asked what that was all about and she shrugged it off as "she didn't think he was good to me and that I should leave him". So not half as dark as was implied!
Another "huh?!" I will add is why did Dennis Pennis shoot Heidi in the cafe? She was cooperating. He wasn't the implied crazed killer we were led to believe from that as later when he had the cop and wife in his house he didn't shoot at them when he had chance!
Yes completely agree that the was not "more to this" faked pregnancy.
I was also expecting something that connected everything together with a twist and was dissapointed by the endings. Highly watchable just finished badly!